Various disorders that affect the cardiovascular system may also impact respiration. For example, heart failure is an abnormality of cardiac function that causes cardiac output to fall below a level adequate to meet the metabolic demand of peripheral tissues. Heart failure (HF) is usually referred to as congestive heart failure due to the accompanying venous and pulmonary congestion. Heart failure may have a variety of underlying causes, including ischemic heart disease (coronary artery disease), idiopathic cardiomyopathy, hypertension (high blood pressure), and diabetes, among others.
Various types of disordered respiration are associated with HF. Respiration rate is linked to the patient's physical condition and is indicative of the patient's disease or health state. In some types of chronic diseases, changes in respiratory rate are gradual over time and may be measured over months or years. However, in heart failure decompensation, increases in respiratory rate can occur over days or weeks. Clinical data collected in the ambulatory setting has demonstrated a statistically significant difference between respiration rate distributions from healthy subjects when compared to patients.
Rapid shallow breathing (RSB) is a typical pattern associated with shortness of breath or difficult breathing (dyspnea: the subjective feeling of being out of breath) caused by heart or lung disorders, strenuous activity, high anxiety or stress. RSB is different from tachypnea (rapid breathing) and hyperpnea (deep breathing). Tachypnea and hyperpnea can occur with hyperventilation, or over breathing beyond what is required to maintain arterial blood gases within normal limits, whereas hyperpnea may be an appropriate increase in breathing such as with exercise. RSB can be associated with symptoms of shortness of breath, or dyspnea. Dyspnea derives from interactions among multiple physiological, psychological, social, and environmental factors, and may induce secondary physiological and behavioral responses. Fear or anxiety may create even more distress in dyspneic patients.
Dyspnea is among the primary factors that reduce patients' quality of life and is a primary reason why many HF patients return to the hospital following a HF decompensation episode. It is estimated that nearly one million hospital admissions for acute decompensated heart failure occur in the United States each year, which is almost double the number admitted 15 years ago. The re-hospitalization rates during the 6 months following discharge are as high at 50%. It is estimated that nearly 2% of all hospital admissions in the United States are for decompensated HF patients, and heart failure is the most frequent cause of hospitalization in patients older than 65 years. The average duration of hospitalization is about 6 days. Despite aggressive therapies, hospital admissions for HF continue to increase, reflecting the prevalence of this malady.